The entire disclosure of Japanese Patent Application No. 2000-142933 filed on May 16, 2000, including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a safety apparatus for a rotary press equipped with an automatic plate-replacing apparatus or the like.
2. Description of the Related Art
In a rotary press, such as a four-color double-sided simultaneous offset printing press, equipped with an automatic plate-replacing apparatus, plate guides of the plate-replacing apparatus are moved from their OFF positions to ON positions and from the ON positions to the OFF positions during automatic plate-replacing operation. However, such automatic plate-replacing operation is hindered if an obstacle is present in (i.e., if a worker or other person enters) a plate-guide work space between printing units at the time of movement of the plate guides.
Accordingly, if an obstacle is placed in the plate-guide work space before or during the automatic plate replacement, it becomes necessary to promptly prohibit starting the automatic plate replacement or to stop the automatic plate replacement.
In view of the foregoing, conventionally, a detector for detecting entrance of a worker or a like person is disposed for each printing unit as a safety apparatus; and the machine is stopped immediately upon detection of such an entrance.
Since the above-described conventional safety apparatus utilizes a detector disposed for each printing unit and adapted to detect entrance of a worker or a like person, components for constituting a detector and a space for installing them must be provided for each printing unit, resulting in increased size and complexity of the apparatus and increased cost.
In view of the foregoing, an object of the present invention is to provide a safety apparatus for a rotary press which can simplify the apparatus to thereby reduce cost and which is suitable for multi-color printing machines.
In order to achieve the above object, the present invention provides an improved safety apparatus for a rotary press. The safety apparatus comprises a detector disposed on a side of a plurality of printing units of the rotary press to cover a zone extending from a furthest upstream printing unit to a furthest downstream printing unit and adapted to detect entry of a foreign object into the zone; a switch provided on each printing unit of the rotary press; and control means for starting operation of the printing units in a next step and detecting operation of the detector when a predetermined time elapses after the switch is operated.
In the safety apparatus, the detector may include a light projecting unit and a light receiving unit; and self diagnosis of the light projecting unit and the light receiving unit may be performed when a predetermined time elapses after the switch is operated. In this case, the self diagnosis of the light projecting unit and the light receiving unit may be performed after completion of the operation of the printing units in the next step.
In the safety apparatus, the operation of the printing units in the next step may be plate replacing operation for removing an old plate from a plate cylinder of each of the printing units and for attaching a new plate to the plate cylinder.
In the safety apparatus, the control means may measure time between operation of the first switch and operation of the last switch. When the time is in excess of a preset time, all the switches are reset.
In the safety apparatus, the control means may stop the operation in the next step when the detector detects a foreign object during the operation in the next step.